Angiotensin II, a main vasoconstrictor hormone of renin-angiotension-aldosterone system (RAAS), plays an important role in pathological physiology of many chronic diseases. The production approach of Angiotensin II which is present in various tissues is mainly as follows: angiotensinogen acted on by renin can be converted to angiotensin I (Ang I) of decapeptide which only has a little activity in contraction of blood vessel; and can be further converted by angiotensin converting enzyme to angiotensin II (Ang II) of octapeptide which is the final physiological active substance of renin-angiotension-aldosterone system (RAS) and can induce physiological functions such as contraction of blood vessel and elevation of blood pressure by binding to specific angiotensin II (ATII) receptor.
EP0253310 discloses a series of imidazole derivatives. It has been found by E. I. Du Pont de Nemours and Company (US) through researches that a compound coded DUP753 has a good effect on lowering blood pressure. It was approved in 1994 and became the first non-peptide type Ang II receptor antagonist, i.e. losartan potassium, which inhibits contraction of blood vessel by selectively blocking the actions of angiotensin II of smooth muscle in blood vessel on its Ang I receptor to achieve the functions of dilating blood vessel and reducing blood pressure.
With development and marketing of losartan potassium, various medical R&D organizations and companies began to study successively on structure of Ang II receptor antagonists. U.S. Pat. No. 5,196,444 discloses a series of benzimidazole derivatives and preparation processes therefor. Such derivatives have angiotensin II antagonistic activity and antihypertensive activity and thereby can be used to treat hypertensive diseases. Among them, candesartan was developed and marketed in 1997 by Takeda Chemical Industries, Ltd. (JP), which releases ester group in vivo and is hydrolyzed to its active metabolite to act on lowering blood pressure.
U.S. Pat. No. 5,616,599 discloses a series of 1-biphenylmethylimidazole derivatives whose structures are similar to that of losartan. The significant difference in structures therebetween is that the chlorine atom at the 4-position of the imidazole ring of losartan is converted to 1-hydroxy-1-methylethyl and the 5-position thereof is converted to a carboxy group, hydroxy group or pro-drug structures such as esters or amides. It is demonstrated to have good activity in lowering blood pressure. Therefore, Sankyo Company, Ltd. (JP) developed and marketed a drug of olmesartan.
PCT/CN2006/001914 described a series of imidazole-5-carboxylic acid derivatives. The characteristic in its structure is that the 5-position of the imidazole ring is converted to an acylal group. This kind of compounds show good activity in lowering blood pressure in animals. Compared with other Ang II receptor antagonists, these imidazole-5-carboxylic acid derivatives have lower toxicity.
However, through studying on a series of imidazole-5-carboxylic acid derivatives, they were found to be hardly dissolved in conventional solvents. Pharmaceutical methods, such as solid dispersion technology, were used to increase the water solubility thereof, which lead to the complexity of preparation technology. Therefore, in order to explore more ideal antihypertensive drugs, there is an urgent need to develop a new form of imidazole-5-carboxylic acid derivatives with good solubility, and applicability for normal preparation technology.